Дата публикации: 14 сентября 2018
Публикатор: Шамолдин Алексей Аркадьевич
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by Igor REZANOV, Dr. Sc. (Geol. & Mineral.), RAS Institute of History of Natural and Technical Sciences (named after S. Vavilov)
Prof. Yuri Mikhailovich Sheinmann (1901-1974), a prominent member of this country's scientific community, begun his studies in the region of Zabaikalye in 1926. And right from the start he made himself prominent with a series of publications on geological problems of Asia. By the mid-1930s he was already a recognized authority in the field of Earth tectonics. When the XVII International Geological Congress met in Moscow in the summer of 1937 Yuri Sheinmann was appointed its scientific secretary. And he made a tangible contribution to the success of this international forum. And shortly after he found himself behind the bars...
AS FATE WOULD HAVE IT
... Winter of 1939-1940. And the scene was the nickel mines of Eastern Siberia scattered in the polar tundra. Convict Sheinmann was serving the second year of his sentence in one of these mines. One day he was summoned to the head office where he was accompanied by prison guards. What happened after was even more surprizing-he was offered to take a seat-an honor unheard of in that place.
- Your name is Yuri Mikhailovich Sheinmann?
- You have a degree of Candidate of Sciences in geology?
- Yes, I do.
- Do you want to work in this field?
- Yes, very much so!
- You are appointed to the management of our Geological Service.
At the end of this short interview the convict was left alone and without guards. He was free to engage in his favourite occupation, and at the first signs of a summer he left on his first geological expedition in 'these latitudes. It was crowned with the discovery of a unique magmatic province in the north of Siberia which contained, among basalts, an exotic complex of volcanic, or igneous rock-ultrabasic and alkaline lavas (he called them meimechites) and carbonates with a high content of calcium and carbon.
His work at the Norilsk Geological Service (which included a course of lectures for geologists) brought him well-deserved recognition-something which must have expedited his release. He was set free in 1945 and remained in Krasno-
yarsk for the next three years before moving to Moscow. He maintained business links with the Norilsk Mining Center for some time before getting a job at what was called the Aerogeologi-cal Trust of the Ministry of Geology. He was appointed head of the Tuva Prospecting Party.
One of the bitter details of his release was that all his personal papers, together with the scientific diploma, had vanished without a trace. His fellow scientists told him that the only possible way of restoring his scholarly status was to defend a thesis for a Doctoral Degree. This he did in 1946 using the materials of his cycle of lectures delivered in Norilsk. His doctoral thesis was entitled "The History of Development of the Siberian Platform".
The degree gave him access to scientific publications and shortly after the prestigious journal Doklady of the USSR Academy of Sciences (proceedings of the Academy) carried his review article on the geological features of the north of the Siberian platform. Another publication of his described some of the unique ultrabasic and alkaline rocks of that region. That same year saw the publication (with a delay of 9 years) of his report at the XVII International Geological Congress. It was carried by the journal Bulletin of the USSR Academy of Sciences. Geological Series" and examined the cycles of folds formation in Eastern and estem Asia.
In the summer of 1949 the country was swept by a new tide of political persecutions which also affected geological scientists. The victims of these reprisals in Leningrad included professors Yakov Edelstein and Mikhail Tetyaev and in Moscow- Academician Josef Grigoryev and Prof. Vladimir Kreiter among others. Yuri Sheinmann shared their fate, but this time around he was exiled to Kolyma, where he was given a rank-and-file job at the Magadan Geological Department where he studied the geological structure of Chukotka. Given access to scientific publications kept at the Department, he was able to prepare a large work on the geological history of the Cordilleras in North America.
His final release and complete rehabilitation came in April 1954. On his return to Moscow, the scientist first got a job with the Aerogeological Trust where he worked before, and later joined the All-Union Institute of Mineral Raws of the USSR Ministry of Geology The five years that followed proved to be a difficult, but also a fruitful time. Being in financial straits, he had to take up translations of scientific monographs (in 1957, for example, the MIR Publishers brought out his translations of a book by the French researcher Du Toite Geology of South Africa). As for his own studies, their results were reflected in an article entitled "Pre-Cambrian Deposits of Tuva", based on the results of his studies while at the Aerogeological Trust, and two more publications on the links of alkaline rocks with mineralization. But the bulk of his energy was dedicated to yet another area of research which somehow remained hidden from the public eye. These were theoretical problems of geotectonics - which had caught his attention back in the 1930s-and studies of regularities in the geological history of this planet. In 1959 these efforts were crowned with the publication of a book Platforms, Folded Belts and Development of the Earth's Structures.
From the late 1950s and to the end of his life Dr. Sheinmann worked at the Institute of Earth Physics (named after 0. Schmidt) of the USSR Academy of Sciences where he was invited by Corresponding Member of the Academy Vladimir Belousov,* a scientist well-known in this country and abroad. Having joined this center, Dr. Sheinmann was given a free choice of his subjects of research, and he was attracted by problems located, so to say, on the bor-
* See: L. loganson, "Geology, His Love", Science in Russia, No. 5, 1997.- Ed.
der of tectonics (studying the structure and evolution of mineral resources of the Earth) and petrology (investigating the in-depth nature of magmatic processes). The crown of the scientists efforts and achievements was a book called Studies of Plutonic Geology (1968) which was translated into English and Japanese.
DEALING WITH GLOBAL PROBLEMS
An interesting feature of the studies of Prof. Sheinmann was his talent of posing scientific problems which retain their importance for decades. And he did this not by way of some theoretical and speculative discussions, but on the strength of some sound, although, sometimes, limited, factual material. It was back in the 1930s that Prof. Sheinmann had established on the basis of his earlier studies in the Zabaikalye Region that the temporal succession of tectonic events in Asia is different from that in Europe and North America. Contrary to the then commonly accepted succession of the tectonic epochs-Caledonian, Hercynic and Alpine (545 min years ago), terminating in global orogenic (folding) processes-Prof. Sheinmann worked out a concept of what he called nonsynchronous development of the eastern and western part of Eurasia.
This approach was fully confirmed in the 1960s by Academician Alexander Yanshin under whose direction a tectonic map of this largest continent was compiled at that time. In his monograph Tectonics of Eurasia (1966) he wrote that "studies of the materials on Eurasia lead one to the conclusion on the absence of not only general planetary phases of folding, but also of the general planetary epochs of such folding- notions which provide the basis of many theoretical conclusions... While working on the map of Eurasia, it was established that the zone of folding of one and the same age can be replaced in its strike by a folding zone of a different age... In all cases, along the strike, or course, of a folded structure we observe the gradually changing age of the upper, and, sometimes also of the bottom border of formations of the same type... The existence of such areas ... underscores even more the absence of universal planetary epochs of increased tectonic activity or epochs of tectonic quiet within narrow time borders."
Thus it took three decades for the ideas of Dr. Sheinmann on an nonsynchronous development of Eurasia to assume the role of a kind of a law in geo-tectonics.
Another, and just as important, idea in this field of geology was formulated by Dr. Sheinmann in his article On the History of the Sinian Shield (1937). In this work he traced the regularities of the tectonic evolution of the Chinese platform (to which the Sinian shield belongs) and its borders and demonstrated for the first time in the world that this, originally single, vast geological structure later disintegrated into separate massif with deep geosynclinal sags (mobile belts) between them. In this way Dr. Sheinmann formulated a new concept of the evolution of the earth crust: platforms characterized by a low intensity of tectonic movements, are modified under the effect of geosynclinal processes.
It should also be pointed out that Dr. Sheinmann formulated these ideas (running contrary to the commonly accepted ones at that time) before the German geologist Hans Stille-a recognized authority in this field, and the Russian scientists-Alexander Peive (later Academician) and Vladimir Sinitsyn. Later on Dr. Sheinmann continued to elaborate these theoretical problems on the materials of the geological history of North America. He was finally convinced of the sound nature of his conclusions when he began an analysis of the most ancient structures of Africa-Archean and Proterozoic (age of more than 545 min years) and then
such structures of other continents. These studies led to the publication of the aforesaid book Platforms, Folded Belts and Development of the Earth' Structures.
Dr. Sheinmann's predecessor, who formulated what can be called an alternative picture of global development, was Dr. G. Stille. In his book Geotectonic Division of the History of the Earth published in 1944 he singled out two great periods in the history of this planet:
Protogaikum (more than 1,800 min years) and Neogaea (late Proterozoic, Paleozoic, Mesozoic and Cenozoic) lasting until now. In his view there occurred between them a major um-bruch, or collapse as a result of which the pan- platform was fractured by geosyn-clinal-folded belts which originated within its confines.
That means that both Stille and Sheinmann were moving practically at one and the same time, and quite independently, towards the basic conclusion of geotectonics concerning the transformation of the platforms. In his book Platforms, Folded Belts and Development of Earth Structures Dr. Sheinmann noted Stille's great contribution to the development of the concept under consideration. At the same time he attacked his theory of "umbruch" which embraced the whole of this planet at one and the same time. "The duration of belts is different and clearly does not obey the regularity suggested by Stille",-wrote the Russian scientist-"Stille's notions of a vast collapse of the platform and the formation of all the geosynclinal areas of the world during one and the same epoch clearly holds no water."
Another major contribution provided by Dr. Sheinmann is related to magmatic geology It was back in Norilsk, as was mentioned before, that he discovered in the north of the Siberian platform a unique magmatic province with ultrabasic and alkaline rocks and carbonatites. This was the starting point in his research on what was then a novel problem-interconnection of tectonics and magmatism. Proceeding from the available material on the Canadian and Baltic shields, the African, Brazilian and Indian platforms, and using his own observations in Siberia, the Russian geologist attacked a common notion that ultrabasic and basic magmas originate from a common source in the bowels of the Earth. Dr. Sheinmann was able to prove that the ultrabasic and basic magmatism develop from different sources which are not interconnected. Originating simultaneously and in parallel, they pass through three stages of a volcanic cycle: the squeezing out (extrusion) of viscous lava; formation of stratified non-differentiated intrusions (penetrating into the earth crust); inclusion into the crust of differentiated intrusions.
In the view of the scientist the ultra-basic melts are directly related to great depths-a notion which later became commonly accepted. And it is this notion, in fact, which is discussed in his article Certain Geological Features of Ultrabasic and Peralkaline Magmatic Formations Upon Platforms, written as early as 1949. But because of its author's arrest, the article was published only in 1955.
Dr. Sheinmann returned to the problem of links between tectonics and magmatism only when he rejoined the Institute of Earth Physics of the USSR Academy. As it turned out this problem could only be resolved only on one condition: if one counts a vast number of the results of chemical analyses of different magmatic rocks. And the scientists embarked on this labour-and time-consuming job of calculations (at some stage in this process he was given an aid which greatly expedited the procedure).
In 1960-1961 Dr. Sheinmann published series of articles on the preliminary results of these investigations, and 1968 saw the publication of his aforesaid monograph- Essays on Plutonic Geology. In this publication data on the processes
in the Earth crust and mantle are compared with the tectonics and chemistry of magmatic phenomena. The author singled out three types of structure of the planet: the greater part of the Earth's surface (which is not subject to contrast movements reaching down to considerably depths); areas under the oceanic undersea ridges, where movements are not very intense and where stretching prevail in the upper core; and a special type of plutonic structure-tectospheres (down to the depth of 600 km). The latter serves as the generator of the basic magmas and through it the energy is released from the bowels of the Earth unto its surface.
Accordingly, Dr. Sheinmann speaks of two areas of fusion of mantle magmas. The first is associated with the layer where matter is close to the melting point which can begin at the slightest upsets of the regime. The second lies in the tectosphere. There the melting is produced by a flux of energy ascending from great depths. The upper- most sections of the mantle and the lower horizons of the core, in the scientist's opinion, are "sterile" with respect to the mantle. The latter is rapidly rising from the depth; as the author of the book points out, "it is better to speak of a torrent of magma, than of a slow rise of asthenolith".
In Dr. Sheinmann's view, there are two types of connection between the formation of primary magmas and tectonics. In one case it facilitates melting and creates conditions for rapid progression of the hot mass up to the surface, and in another case melting depends on the energy of the plutonic tectonic process. In other words, there are magmas of what we call relative rest and there are magmas of active and deeply lying areas which are very "energy-intensive".
And it is important to bear in mind that all of these ideas were put forward more than three decades ago, when isotopic studies of these processes were only starting same as deep-sea drilling and dragging of ocean floor.
The way we see it now, Dr. Sheinmann's theories on the interdependence of tectonics and magmatism need some reappraisal. But there is no denying the fact that in the 1960s he was the first to try and provide a global assessment of terrestrial magnetism, identity the problems involved and map out the likely solutions.
For an assessment of Dr. Sheinmann's contribution to the geological science it is best to try and compare him with his German counterpart Dr. Stille. And although he was 25 years older than Dr. Sheinmann, their lines of research often crossed. And here I am not trying to equate the two recognized leaders in the studies of geotectonics-Dr. Stille's contribution is greater. But the way I see it, if not for the two violent breaks in the research career of Dr. Sheinmann, he would have accomplished much more, matching the legacy of his universally recognized German colleague.
Russian biologist A. Lyubishchev once said that the past of science is like a collection of unfinished architectural ensembles. And I could add to that metaphor that it was Dr. Yuri Sheinmann who laid the foundations of several such monuments.
Опубликовано 14 сентября 2018 года
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